Spring on engine mount.

[Ian Williams]

Agreed Alan, to stiffen the chassis properly takes considerably more work than simply bolting the engine down hard, I have however never seen a crankcase with broken feet from NORMAL use. If we want to talk about weak crankcases we probably need to look at that relative to how lightly the rest of the car is built, when it was designed and what it was all designed to do.

[Austin in the Shed]

Use the later rubber mounts except the one that's through the middle of the c/case and yes nylocs or double nuts at the back.
At the front slightly longer bolts trimmed to a length that pinches the rubber washers when they bottom out on the blind threaded holes in the forged nose of the chassis.
I had a crankcase a couple of years ago to convert. On looking at it closely both front mountings had been sheared out of the case and gas welded back together.I would suspect it was serious accident damage rather than chassis flex though.

[Reckless Rat]

Over the years I have replaced several sets of rubber mountings on the engine of my RP ( it has a later 2brg rubber mounted crankcase). For minimum vibration and longevity I have discovered a couple of factors that are important in my view. Firstly, sort out the oil leaks because impregnation causes the rubbers to blow and split. Secondly, don't overtighten. That also exerts pressure on the top rubbers and reduces their life.

Last year I experimented with a set of polybushes turned from a length of poly bar. It is a harder compound than the rubber and supposedly fuel and oil proof. To this set of bushes I added a spring at the rear nearside. They lasted about a month before they started to break up.

So, after the engine rebuild I fitted yet another set of rubber mounts to an engine which now had been rendered oil tight. The mounting bolts, which are fitted with nyloc nuts were just done up enough to pinch the rubbers without crush. The car has done about 3000 miles since then with no apparent degradation. A result in my opinion. Centre rubbers still in place.

[Renaud]

Renaud,

A bolt has a threaded portion at the bottom, followed by a plain shank up to the head., unlike a setpin, which is threaded all the way up its length.

A bolt " bottoms out" when one puts a nut on the reaches the end of the threaded portion without putting any tension on whatever the bolt passes through.

Hope this helps (and no, you are not a 'silly frog' - English is the most awkward of languages with lots of obscure idioms!)

Thanks David, always happy to learn those obscure idioms!
So do I understand that "longer bolts bottomed out at the front" means that there is play left under and the nut is not secured on the chassis? In other words the bolt is only there to keep the crankcase in line?
(Still frog but little less silly now maybe)

[David Stepney]

Renaud,

A bolt has a threaded portion at the bottom, followed by a plain shank up to the head., unlike a setpin, which is threaded all the way up its length.

A bolt " bottoms out" when one puts a nut on the reaches the end of the threaded portion without putting any tension on whatever the bolt passes through.

Hope this helps (and no, you are not a 'silly frog' - English is the most awkward of languages with lots of obscure idioms!)

Thanks David, always happy to learn those obscure idioms!
So do I understand that "longer bolts bottomed out at the front" means that there is play left under and the nut is not secured on the chassis? In other words the bolt is only there to keep the crankcase in line?
(Still frog but little less silly now maybe)

Exactement, mon ami!

[Peter Clayton]

I always thought that "bottoming out" was when a setscrew/bolt/stud etc. was put into a blind hole and was screwed in until the Bottom of the hole was reached . Have I been wrong all these years? Maybe an old dog can be taught.

[Tony Griffiths]

Use the later rubber mounts except the one that's through the middle of the c/case and yes nylocs or double nuts at the back.
At the front slightly longer bolts trimmed to a length that pinches the rubber washers when they bottom out on the blind threaded holes in the forged nose of the chassis.
I had a crankcase a couple of years ago to convert. On looking at it closely both front mountings had been sheared out of the case and gas welded back together.I would suspect it was serious  accident damage rather than chassis flex though.

Thanks; of course, the front mounts are blind holes. I'd forgotten that!

[Austin in the Shed]

Just to make it clear that these mods are on the earlier solid mount crankcase,That's why I wasn't using the middle rubber.
If using these later rubbers in a standard car with the starting handle still used  you may have to thin the one down between the crankcase and chassis as it may raise the engine too high to go through the hole in the radiator shell.

[John Mason]

Peter I think it amounts to the same thing. Although the bolt with nut tight or set screw in a blind hole tight because the stud can go no further. They both leave whatever you are trying to attach loose on either stud or bolt. Your stud in a blind hole does fit the term better however.

John Mason,